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devmap_contextmgt - driver callback function for context management

#include <sys/ddi.h>
#include <sys/sunddi.h>



int devmap_contextmgt(devmap_cookie_t dhp, void *pvtp,
 offset_t off, size_t len, uint_t type, uint_t rw);

illumos DDI specific (illumos DDI). dhp pvtp off len type rw devmap_contextmgt() is a driver-supplied function that performs device context switching on a mapping. Device drivers pass devmap_contextmgt() as an argument to devmap_do_ctxmgt(9F) in the devmap_access(9E) entry point. The system will call devmap_contextmgt() when memory is accessed. The system expects devmap_contextmgt() to load the memory address translations of the mapping by calling devmap_load(9F) before returning.

dhp uniquely identifies the mapping and is used as an argument to devmap_load(9F) to validate the mapping. off and len define the range to be affected by the operations in devmap_contextmgt().

The driver must check if there is already a mapping established at off that needs to be unloaded. If a mapping exists at off, devmap_contextmgt() must call devmap_unload(9F) on the current mapping. devmap_unload(9F) must be followed by devmap_load() on the mapping that generated this call to devmap_contextmgt(). devmap_unload(9F) unloads the current mapping so that a call to devmap_access(9E), which causes the system to call devmap_contextmgt(), will be generated the next time the mapping is accessed.

pvtp is a pointer to the driver's private mapping data that was allocated and initialized in the devmap_map(9E) entry point. type defines the type of operation that device drivers should perform on the memory object. If type is either DEVMAP_LOCK or DEVMAP_UNLOCK, the length passed to either devmap_unload(9F) or devmap_load(9F) must be same as len. rw specifies the access direction on the memory object.

A non-zero return value from devmap_contextmgt() will be returned to devmap_access(9E) and will cause the corresponding operation to fail. The failure may result in a SIGSEGV or SIGBUS signal being delivered to the process.

0 Non-zero Example 1 managing a device context

The following shows an example of managing a device context.

struct xxcontext cur_ctx;
static int
xxdevmap_contextmgt(devmap_cookie_t dhp, void *pvtp, offset_t off,
 size_t len, uint_t type, uint_t rw)
{
 devmap_cookie_t cur_dhp;
 struct xxpvtdata *p;
 struct xxpvtdata *pvp = (struct xxpvtdata *)pvtp;
 struct xx_softc *softc = pvp->softc;
 int err;

 mutex_enter(&softc->mutex);

 /*
 * invalidate the translations of current context before
 * switching context.
 */
 if (cur_ctx != NULL && cur_ctx != pvp->ctx) {
 p = cur_ctx->pvt;
 cur_dhp = p->dhp;
 if ((err = devmap_unload(cur_dhp, off, len)) != 0)
 return (err);
 }
 /* Switch device context - device dependent*/
 ...
 /* Make handle the new current mapping */
 cur_ctx = pvp->ctx;

 /*
 * Load the address translations of the calling context.
 */
 err = devmap_load(pvp->dhp, off, len, type, rw);

 mutex_exit(&softc->mutex);

 return (err);
}

devmap_access(9E), devmap_do_ctxmgt(9F) devmap_load(9F), devmap_unload (9F)

Writing Device Drivers